Prior art whiteboards or electronic boards allow a user to handwrite on a writing surface such as a sheet using a certain writing instrument, and an onboard scanner scans the handwritten information. Furthermore, the scanned information is later printed on an image-recording medium via a printer. In more recent years, the electronic boards have a coordinates input/detection unit on a writing surface for inputting the hand written information into a computer on a real time basis. For example, Micrographic, Inc. offers an electronic whiteboard with an onboard input/detection unit on the writing surface for inputting the hand written visual data such as characters and pictures into a computer on a real time basis. The same electronic board system allows to display on a cathode ray tube (CRT) or a large screen using a liquid crystal projector the visual data stored in the computer from the electronic board. The visual data is also printed on an image-recording medium. Furthermore, a softboard is connected to a computer, and a computer screen is projected onto the softboard via a liquid crystal projector. A user operates the computer on the softboard.
Another type of electronic board includes a display unit for displaying characters and images; a touch panel/screen or coordinate input/detection unit located in front of the display unit for inputting and detecting the coordinate information; and a control unit for controlling the display unit based upon the input from the coordinate input/detection unit. Based upon the above units, the electronic board provides a display surface and a writing surface. For example, SMART Technologies Inc. offers SMART 2000, which projects characters, pictures, diagrams and graphic images onto a projection panel via a liquid crystal projector that is connected to a computer and inputs into the computer any hand-written information via the coordinate input/detection unit or the writing surface located in front of the projection panel. The hand-written information is then composed with the image information in the computer, and the composed image is again displayed via the liquid crystal projector on a real time basis.
The above described electronic blackboard systems superimpose the image from the coordinate input/detection unit over another image displayed on a screen by the display unit. Because of the superimposing feature, the electronic blackboard systems are already widely used in conferences, presentations and education, and the use is evaluated to be highly effective. Furthermore, certain electronic blackboard systems incorporate telecommunication such as audio and video features and provide videoconferencing capability for connecting remote locations via a communication line.
Various types of the coordinate input/detection units have been considered. Among various detection techniques, a coordinate input/detection device using an optical system and involving no physical surface such as a touch panel appears to be promising for the application to the above electronic blackboards. Optical coordinate input/detection devices have been proposed and used with various methods. For example, Carol Touch Co. offers Model 42 plasma display infrared touch panel frame for placing on the Model 42 display. A plurality of light-emitting diodes (LEDs) is placed in rows and columns at equal distance in both horizontal and vertical directions. Similarly, a plurality of phototransistors is placed in both horizontal and vertical arrangements at the same distance. By continuously scanning pairs of a LED and a phototransistor, it is checked if infra red light is interrupted in either X and or Y directions. Upon detecting the interruption of the infra red light, the corresponding coordinates are determined and then outputted to an external device. According to Japanese Patent 2705156, a plurality of pairs of a light emitting element and a light detecting element are placed from the upper left to the lower right as well as from the upper right to the lower left in a diagonal direction. Each of the light detecting elements detects light from two corresponding light emitting elements by time-dividing the detection. Furthermore, according to Japanese Patent 2980286, diffused light from a light source located near a central or terminal one of a single row of light detecting elements is reflected by a holographic reflector located to form parallel light. A plurality of the light detecting elements on the light source side receives the parallel light.
Using a coordinate input detection device such as the above described Carol Touch Inc.'s device having conventional light emitting elements such as LEDs and light detecting elements such as phototransistors, a detection path or line between the light emitting element and the light detecting element is parallel to those of other pairs. For this reason, the input resolution of the input coordinates depends upon the distance between the light emitting element and the light detecting element. In other words, in order to increase the resolution, the distance between the light emitting element and the light detecting element must be reduced. However, there is a limitation in decreasing the above distance, and the resolution cannot be substantially improved.
As described above, Japanese Patent 2705156 discloses that one light detecting element receives light from two light emitting elements by time division. Since the light paths for all of the light detecting elements are parallel in two directions, although there is a difference between horizontal/perpendicular relations and diagonal relations, as described with respect to the Carol Touch device, the resolution on the coordinates still depends upon the size of and the distance between the light emitting element and the light detecting element. For this reason, if a high resolution is required, the conventional coordinate input devices remains to be improved.
As described above, Japanese Patent 2980286 discloses that there is a diffused light path from a single light emitting element towards a holographic reflector in addition to parallel light paths between the holographic light reflector and each of the single row of the light detecting elements. However, the light detecting elements in certain areas near the holographic reflector do not receive light reflected by the holographic reflector. Due to the above area where coordinates are not determined from the interruption of the diffused light, if a high resolution level is required in a large area, the conventional coordinate input devices remains to be improved. That is, in the area near the holographic reflector, the resolution is determined by the placement distance of the light detecting elements. Furthermore, since the interruption of the path between the holographic reflector and the light emitting element or the interruption of the path between the holographic reflector and the light detecting element is detected by the same light detecting element, it is difficult to determine the true interruption position.
Accordingly, the current invention involves a plurality of light emitting and detecting elements that are placed in two directions to cross and surround a two-dimensional coordinate input and detection unit which receives a command from a operational unit so that input coordinates are determined at a high resolution level for the electronic blackboard. The current invention also improves efficiency for the coordinate determination by eliminating any unnecessary calculation processes.